1. Field of the Invention
The present invention is directed to a signal-processing device for hearing aids of the type having a signal line for the transmission of a signal to a hearing aid amplifier and having a control device for the connection and disconnection of the hearing aid signal source. The present invention also is directed to a hearing aid having one or more of these signal-processing devices as well as to a method for the operation of the signal processing devices. What is thereby understood by a signal-processing device means any device that can serve as signal source for the hearing aid amplifier.
2. Description of the Prior Art
A number of internal and external signal sources can be connected to a hearing aid system. Microphones and telephone coils with or without an integrated pre-amplifier and/or an integrated analog-to-digital converter are examples of such signal sources. Due to the limited energy supply possibilities, the problem of being able to connect and disconnect individual signal sources—possibly with their signal processing devices—separately from one another. In the case of a disconnect, the signal sources should be placed into a condition that results in a low power consumption (standby mode).
A fundamental idea for solving the problem is to reduce the power consumption, i.e., the signal sources are shut off by the hearing aid amplifier when they are not required. Techniques are known for this purpose.
When the signal sources or signal processing devices are fed via a common supply line, then they can be deactivated in common by shutting off the supply voltage. Likewise, all signal sources can be activated by the common supply line being supplied with voltage.
When the individual signal sources are provided with separate supply lines, then each individual source can be separately connected to or disconnected from the hearing aid amplifier. In this case, however, individual supply lines must be provided from the hearing aid amplifier to each signal source. Additional lines as well as additional terminals at the hearing aid system are thus required.
When the individual signal sources are in fact centrally supplied with voltage but are connected to the hearing aid system by additional signal lines, then it is likewise possible to connect or disconnect individual signal sources. The disadvantage that additional lines and terminals must be provided, however, also exists in this case.
In this context, German Published Application 2 313 108 discloses a circuit for the power supply of amplifiers, wherein an input signal is amplified in a pre-amplifier that is fed from a supply source. The output signal of the pre-amplifier is supplied to the amplifier and control means. When the control means find that the first signal has arrived at the input, then the amplifier is driven with a high feed current. When the control means find that the second signal has arrived at the input, then the feed current for the amplifier is set to the economy power value. The amplifier amplifies the output signal of the pre-amplifier, whereas the output signal of the amplifier is reproduced in a playback device, for example a speaker.
Further, Japanese Patent Application 60 123 198 discloses a hearing aid that has a specific circuit for reducing the power consumption. A detector circuit compares the output level of a high-frequency amplifier to a reference voltage and emits an output signal with a high level when the output level is higher than the reference voltage. A voltage supply disconnect circuit activates a switch element only when the detector circuit generates the signal with high level and thus applies the battery voltage to the electrical circuitry of the hearing aid. The battery voltage is disconnected given too low an output level of the amplifier, in order to reduce the power consumption. This Japanese application, however, is directed only to a hearing having one signal source or one signal-processing path.